I am not an upper level eventer by any means, but I rarely counted my strides out XC. To me, there’s way too many variables to accurately be able to gauge exactly how many strides: terrain, depth of grass/terrain/traction, the horse’s natural length of stride, quality of canter coming in, the type of fence before/after, etc – of course, I would walk the combinations a few times to get a good idea of the distance, but to me, the quality of the canter is more important than the number of strides between elements. Some horses are not physically capable of having a 12 foot stride,
Focus on the balance and impulsion of the canter in gridwork, and do that often enough (combined elements) and your horse will start to plan ahead for you – I know some riders don’t incorporate grid work or combined elements as much as they could or should – but a well trained horse is adjustable without you needing to micromanage it. They look for the next fence while they are in midair, same as us – and a good horse can figure out his own striding… which kind of goes part and parcel with the fifth leg; some horses need to learn to be more autonomous cross-country. It’s one of the reasons I spend more time getting my green beans going over XC fences in hand or on the lunge so that they start to answer the problems for themselves without ‘mommy’ holding their hands – and then I ask the same of them under saddle. I let them struggle a bit, make a mistake or two, and then go back to doing something easy like a coop or a log. I find a lot of riders when focusing on meeting a combination, might micromanage and pull back on their mounts’ face too much – which makes the mount want to rush, chip in, or suck back – none of which can help the horse get the proper impulsion and balance it needs to clear the fence safely. Focus too much on getting the pretty stride makes some riders get too in their horse’s face XC.
I think that counting strides out on cross country is better left in the schooling ring (to practice adjustability) where everything is predictable: the footing most important. If you pay attention to top riders like Jung, WFP, IK, etc, you’ll notice that they have mentioned that they don’t focus on counting strides, they focus on delivering a good canter up to the fence.
So to answer your question – be careful about focusing too much on counting strides, otherwise you lose the impulsion you need, which directly affects the horse’s balance and speed: to jump cleanly and safely, the horse needs a balance of these three principles and it’s more important to focus on achieving that balance than to focus on the metric distance a stride should have.